What causes psychosis symptoms in Parkinson's disease?

Psychosis is a collection of symptoms that occur when a person’s mind loses connection to reality. These symptoms include sensing things that are not real (hallucinations), believing things that are not true (delusions), and misinterpreting real objects in the environment (illusions).

Parkinson’s disease (PD) psychosis is psychosis caused by having Parkinson’s disease, a neurodegenerative disorder that primarily causes uncontrolled and involuntary movements—but also causes a wide variety of other symptoms, including symptoms that affect cognition, mental health, and physical health.

PD psychosis can occur at any stage of Parkinson’s disease, even the early stages—and in some cases, before the initial movement-related symptoms begin. However, it is more likely to occur as the disease progresses.

To understand the causes of PD psychosis, it helps to understand what is happening in the nervous system when a person has Parkinson’s disease.

What causes PD?

The exact cause of PD is unknown. Between 15 and 25 percent of cases are linked to family history, but the majority of cases occur in people with no family history of the disease. Research supports the idea that PD is caused by a combination of genetic predisposition and exposure to environmental factors—specifically, industrial chemicals used in agriculture, mining, and manufacturing. The incidence of PD is higher in regions with a history of these industries.

Although we do not know why some people develop PD and others do not, research has given us a good understanding of what is happening in the brain and nervous system when a person has PD. In the simplest terms, PD causes damage to neurons (nerve cells).

Neurons can be thought of as the body’s communication cells. They conduct the electrical impulses the brain and spinal cord use to send signals to the rest of the body. They also produce neurotransmitters, chemicals that enable and control this kind of signaling. Voluntary and involuntary movements, breathing, digestion, heart rate, blood pressure, and countless other functions all rely on neurons.

Neurodegenerative diseases like PD cause neurons to stop working and die off, resulting in physical and chemical changes in the brain, altering how the brain works.

What sets PD apart from other neurodegenerative diseases is where this damage occurs—primarily in the regions of the brain that control movement. (However, the damage caused by PD can extend to other regions as the disease progresses.)

What causes PD psychosis?

Though the mechanism of PD psychosis is not fully understood, it is believed to be a result of the physical and chemical changes to the brain that occur as a result of Parkinson’s disease. Medications and other factors may also contribute to psychosis symptoms.

Medications

The main therapies for Parkinson’s disease are medications that act on dopamine and other neurotransmitters. These medications may exacerbate psychosis symptoms in some cases, but psychosis symptoms also occur without these medications. A person with Parkinson’s disease should never stop taking a medication unless directed to by their healthcare provider.

Other risk factors

Additional risk factors associated with PD psychosis include:

• Cognitive impairment (problems with memory, thinking, and cognition), especially dementia
• Sleep disorders, such as insomnia and rapid eye movement (REM) sleep behavior disorder, which causes a person to physically act out vivid and unpleasant dreams
• Having Parkinson’s disease for a longer time and/or having more advanced Parkinson’s disease
• Delirium, a severe (but reversible) state of severe confusion and disorientation that can be caused by coexisting medical conditions, nutritional deficiencies, and medication side effects
• Vision problems
• Depression
• Older age

There are therapies that can ease and manage the symptoms of PD psychosis. Treatment begins with an evaluation by a healthcare provider—and if you or a loved one is experiencing psychosis symptoms, it’s important to discuss those symptoms with a healthcare provider. The first step in treatment should always be evaluation.